The present invention relates to a method of producing an integrated circuit configuration in which active regions are surrounded and insulated by trenches filled with insulating material.
Increasingly, integrated circuits are configured in which active regions are insulated from one another by trenches which are filled with insulating material and surround the active regions. In this specialist area, such insulation is called shallow trench isolation (STI).
To produce an integrated circuit with shallow trench isolation, trenches defining active regions are first etched in a main surface of a semiconductor substrate. The trenches are then filled with insulating material. One problem with this is the formation of a planar surface over the whole semiconductor substrate.
A proposal has been made (see B. Davaria et al., IEDM 89, pages 61 to 64), for filling the trenches, to start by depositing a first insulating layer, which is planarized by chemical mechanical polishing using a photoresist mask and a planarizing lacquer layer. In this case, the photoresist mask has structures covering the low-lying surface zones of the insulating layer. This ensures that the planarizing second photoresist layer has only slight surface variations, which can be compensated for during chemical mechanical polishing. In this method, the photoresist mask is generated from the mask used to produce the trenches, the pattern of the photoresist mask corresponding to the pattern of the trenches, but the lateral measurements of the patterns in the photoresist mask being reduced by a lateral allowance in comparison with the width of the trenches. Since a minimal structure width dependent on the respective technology cannot be undershot when the photoresist mask is formed, the trenches in any zones of the photoresist mask in which the pattern, defined using the trench pattern, of the photoresist mask does not fulfill this condition will be underfilled or overfilled, which has disadvantageous consequences for the planarity that can be achieved.
It is accordingly an object of the invention to provide a method of producing an integrated circuit configuration which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which greater planarity is achieved than in the prior art.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing an integrated circuit configuration, which includes the forming of trenches surrounding active regions in a main surface of a semiconductor substrate. Applying a photoresist layer to the insulating layer and structuring the applied photoresist layer to form a mask, using a data processing device, by the following steps:
providing an idealized pattern representing trenches formed in the semiconductor substrate and having contours which correspond to contours of the trenches and having idealized active regions which represent the active regions in the semiconductor substrate;
producing an idealized mask pattern on the basis of the idealized pattern containing rectilinear contours which are shifted by an allowance in comparison with the idealized pattern, the allowance starting on that side of the idealized active regions which is respectively remote therefrom, the idealized mask pattern having surface zones defined therein which are bounded by the rectilinear contours whose distance apart is shorter than a given minimum measurement; and
using the idealized mask pattern to produce a further idealized mask pattern in which the surface zones are replaced by minimum surface elements having length measurements which are greater than the given minimum measurement where a surface of the minimum surface elements essentially corresponds to a surface of the surface zone which the minimum surface elements are replacing, and where the mask is formed from the further idealized mask pattern.
Filling the trenches by depositing an insulating layer using the formed mask.
In one embodiment of the method, the idealized mask pattern has surface regions defined in it which are spaced apart from adjacent surface regions by a distance which is greater than the prescribed minimum measurement, and replacing surface zones arranged in these surface regions by the minimum surface elements.
In another embodiment of the method, the surface zones whose surface is smaller than the surface of a minimum surface element are replaced by the minimum surface element, controlled on the basis of a probability corresponding to the quotient formed by the surface of the surface zone and the surface of the minimum surface element.
In another embodiment of the method, having the step of planarizing the insulating layer by chemical mechanical polishing after the further photolayer has been applied.
In another embodiment of the method, the prescribed minimum measurement is at least as large as the length of a smallest structure which can be produced in the mask, and in that one of the minimum surface elements is rectangular, the sides of the rectangle having a length which is respectively at least as great as the length of the smallest structure which can be produced in the mask.
In the method, trenches defining active regions are produced in a main surface of a semiconductor substrate. The trenches are filled by depositing an insulating layer and by a planarization process, using a mask. The mask is produced in that, on the basis of the pattern of the trenches, a data processing device is used to define an idealized pattern which represents the semiconductor substrate""s structures to be planarized. This pattern is used to define an idealized mask pattern. This idealized mask pattern contains raised structures which correspond to the pattern of the trenches but whose measurements are reduced parallel to the main surface by a lateral allowance in comparison with the measurements in the pattern of the trenches. This means that the rectilinear contours or the edges in the idealized mask pattern point in the direction away from the active regions enclosed by the trenches. The allowance starts on that side of the contours which is not situated on the same side as the adjoining active region. The idealized mask pattern subsequently has surface zones defined in it, in the data processing device, whose measurement in at least one dimension parallel to the main surface is smaller than a predetermined minimum measurement. The distance between the rectilinear contours forming the surface zone at least on two opposite sides is shorter than the minimum distance. The overall contour of the surface zone is composed from respectively rectilinear portions. The data processing device replaces these zones in the idealized mask pattern by auxiliary structures which have minimum surface elements. This finally produces a further idealized mask pattern. In the dimensions or directions parallel to the main surface, the minimum surface elements each have length measurements or lateral lengths of at least one predetermined minimum measurement. In this instance, the sum of the surfaces of the minimum surface elements in an auxiliary structure corresponds essentially to the surface of the surface zone in the idealized mask pattern, which surface zone is replaced by the respective auxiliary structure. The predetermined minimum measurement will in practice be essentially the same as the structure size which can be produced as a minimum in the respective technology. The further idealized mask pattern, obtained from the data processing device, is converted into the mask formed from the photoresist on the semiconductor substrate.
The surfaces of the minimum surface elements have a minimum surface defined by the minimum measurement, since the respective lateral length of the minimum surface is greater than the minimum measurement. The distance between opposite sides is greater than the minimum measurement. The minimum surface elements can also be larger than this minimum surface. The minimum surface elements are of rectangular design. Each side of the rectangle is longer than the minimum measurement. The surface zones to be replaced are likewise rectangular. They are delimited on at least two opposite sides by contours of the idealized mask pattern. In this case, the distance between these at least two opposite contours is shorter than the minimum distance.
The idealized mask pattern""s surface zones in which, in one dimension or direction, the measurement is smaller than the predetermined minimum measurement are zones in which the trenches are underfilled in the method known from the prior art. The predetermined minimum measurement is at least as large as the shortest length of a structure which can be produced in the mask. A minimum surface element is rectangular, and the lateral lengths of the rectangle are each of a length having at least the predetermined minimum measurement, that is to say being at least as long as the length of a smallest structure which can be produced in the mask.
The invention solves this problem in that, in the idealized mask pattern, these surface zones are provided with minimum surface elements whose overall surface essentially corresponds to the surface of the zone replaced by the minimum surface elements. In this context, the invention makes use of the realization that optimum planarization is essentially dependent on the surface coverage being essentially constant over the main surface. The idealized mask pattern fulfills this condition. It is infringed again only by the additional conditions of the technology with regard to minimal structure width. Replacing such zones, according to the invention, with the auxiliary structure described ensures uniform surface coverage, however. Defining the auxiliary structure requires only two dimensions to be considered.
The idealized mask pattern is defined automatically on the basis of the pattern of the trenches, the lateral allowance and the predetermined minimum measurement, using a data processing program running on a computer.
With regard to the quantity of data to be processed and the computation time required, it is advantageous to define surface regions in the idealized mask pattern which are each surrounded by a structure whose measurements parallel to the main surface are larger than the predetermined minimum measurement. This means that two adjacent regions are spaced apart by a distance in length which is longer than the minimum distance. On the other hand, such a surface region can contain trench contours which enclose individual active regions and whose distance apart is shorter than the minimum measurement. The minimum surface elements are the kind which are delimited on at least two opposite sides by mask contours. The auxiliary structures are then defined in these regions in each case. This considerably reduces the quantity of data to be taken into account. In addition, parts of the mask are prevented from being processed in which there is no infringement of the condition regarding the minimum measurement.
According to one refinement of the invention, zones whose measurements in at least one dimension parallel to the main surface are smaller than the predetermined minimum measurement and whose surface is smaller than the surface of one of the minimum surface elements are replaced in the data processing device by a minimum surface element with a probability corresponding to the quotient formed by the surface of the zone and the surface of the minimum surface element. This means that replacement is controlled on the basis of probability. If, gradually, one of these surface zones after the other is regarded in the data processing device, for example, then a replacement by a minimum surface element is made or is not made on the basis of a probability generator. The parameter controlling the probability generator is the quotient of the surface of the surface zone and the surface of the minimum surface element. The probability control is thus based on the quotient of the surface zone whose surface is smaller than that of a minimum surface element and the minimum surface element. This results in photoresist starting to be deposited, said deposit having minimum surface elements and having, to some extent xe2x80x9con averagexe2x80x9d, a proportion of photoresist which corresponds to the surfaces of the surface zones. In this context, the desired condition that the structure sizes be greater than F and that the surface sizes be greater than Fxc3x97F is observed. This compensates for errors which, if these zones with a small surface were neglected, would arise particularly in those parts of the mask in which a number of excessively small zones are disposed at regular intervals.
Planarization can involve any known planarization methods which use a mask to compensate for unevenness in a surface that is to be planarized.
According to one refinement of the invention, the mask is formed from a first photoresist layer. The mask is derived from the idealized mask structure ascertained in the data processing device using the steps described above. A second, flowing photoresist layer is subsequently applied to this mask. The surface of the substrate is then planarized by chemical mechanical polishing. Chemical mechanical polishing is ended as soon as the main surface of the substrate has been reached. To protect the active regions, it is advantageous in this case to provide them with a protective layer made of silicon nitride or silicon oxide before the trenches are etched.
According to a further refinement of the invention, the insulating layer is structured using the mask. This produces insulating structures in the trenches. A flowable insulating layer, preferably a glass layer, is subsequently deposited and made to flow. This achieves planarity for the structure. To expose the surface of the active regions, the glass layer which has flowed can be back-etched isotropically or anisotropically.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in method of producing an integrated circuit configuration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.